Hello,
To get access to OCCT repo, you need to register on OCCT dev portal and sign CLA, see https://dev.opencascade.org/index.php?q=home/get_involved
Alas, we at OCC have no experience of preparing Debian packages for OCCT.
Having ready-to-use OCCT packages for Ubuntu and Debian is interesting for us and we will try to help you if particular questions appear.
You are welcome to use OCCT dev forum (https://dev.opencascade.org/index.php?q=home/forum) to share your progress and discuss any topics on OCCT.
Best regards,
Commenter-1